Milan became a self-governing imperial city by the peace of Constance
1183. Although Milan was a republic it was usually dominated by one person,
a so called signore. The political life was characterised by internal strife
between the Guelfs led by the house of della Torre who supported the pope
and the Ghibbellins led by the house of Visconti who supported the emperor.
During the numerous wars in the 14th and 15th
centuries Milan conquered several of its neighbours and became master of
Lombardy. Giovanni Galeazzo Visconti purchased a ducal title from the
emperor 1395 whereby Milan formally seized to be a republic. During the the
Italian Wars in the 16th century Milan was constantly fought over
and were often under French control. When the house of Sforza died out 1535
Milan came under the Habsburgs rule, which with the exception of two periods
would last until the unification of Italy in the middle of the 19th
century.